<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>Document</title>
</head>
<body>
  <script>
    function Foo() {
      this.a = 123;
    }
    let obj = {};
    let Bar = Foo.bind(obj);
    let b = new Bar();
    //? Foo this ???  
    // new 的优先级 > call/apply/bind
    </script>
</body>
</html>